The present invention relates to space frames, that is three-dimensional frame structures and in particular such structures for use in the building industry.
Space frames for use in the building industry for, for example, supporting the floors or roofs of buildings, comprise upper and lower grids of chords which are interconnected by bracing members.
Hitherto, the bracing members of such space frames have been fully triangulated. However with such structures, the bracing members form an obstruction to service ducting etc, which desirably may be located within the space frame between the upper and lower grids of chords.
UK Patent Application No GB 2054694 discloses a modular space frame assembly in which the nodes of the upper and lower grids are interconnected by vertically extending bracing members. This provides excellent access for service ducting to run in both grid directions.
However, such structures suffer weight penalties in comparison to optimally designed triangulated space frame structures proposed hitherto, due to the need for the chords to resist bending moments and shearing forces, in addition to dominant axial forces found in triangulated space frame structures. Moreover, the vertical bracing members are required to primarily resist bending moments and shear forces, instead of the dominant axial forces of triangulated structures, requiring heavier sections than the bracing members of triangulated structures.
According to one aspect of the present invention, a space frame comprises upper and lower grids of intersecting chords, bracing modules interconnecting the upper and lower grids in spaced apart relationship, the bracing modules being spaced apart from one another in each grid direction, the bracing modules comprising four intersecting bracing members, the bracing members arranged in mutually inclined pairs, the bracing members of each pair extending between upper and lower chords in the same grid direction, each pair of bracing members crossing the other pair of bracing members, the point of crossing of each pair of bracing members coinciding with or being positioned between each member of the other pair of bracing members and either the upper or lower chord associated with the other pair of bracing members.
In space frame structures according to the present invention, unobstructed, full depth voids are provided between the upper and lower grids, running in each grid direction, to permit improved access for service ducting etc, compared to triangulated structures. By using pairs of inclined bracing members, individual bracing members are loaded primarily in axial tension and compression and yet are capable of adequately accounting for the applied chord shears, moments and axial forces and by adjusting the points at which the bracing members intersect the upper and lower chords the moments in the chords can be conveniently adjusted to suit the available load carrying capacity of the chords. As a result, lighter section chords and bracing members may be used.
According to a preferred embodiment of the invention the chords forming each grid are offset, those chords arranged in one direction of the grid being mounted on top of the chords arranged in the other direction of the grid. In this manner, the grids may be formed from continuous chords extending in each direction of the grid. Alternatively, the chords forming each grid may be co-planar, the chords being jointed in suitable manner, at the nodal points at which the chords intersect.
In a further embodiment, for the upper grid, the chords in one direction may be spaced vertically above and secured to the upper surface of the chords in the other direction; while for the lower grid, the chords in said one direction may be spaced vertically below and secured to the lower surface of the chords in said other direction.
In a preferred embodiment of the invention, the bracing modules are located at the nodal points of the grids, the bracing members being secured to the chords, in spaced-apart relationship, between the nodal points. Alternatively, the bracing modules may be arranged such that each bracing member extends between a nodal point on one grid and a diagonally opposed nodal point on the other grid, the bracing members intersecting at the point of intersection of diagonals joining four adjacent nodal points on one grid to four adjacent nodal points on the other grid.
The bracing members constituting the bracing modules may be interconnected at their point of intersection or may be offset from one another.